Antioxidant Vitamins Status in Wistar Rats with Induced Thyroid Dysfunction

Oxidative stress plays an important role in the pathogenesis of thyroid disorders. Major effects of thyroid hormones are the acceleration of mitochondrial respiration which is accompanied by excessive production of reactive oxygen species leading to oxidative stress and lipid peroxidation. The current study examined the status of serum antioxidant vitamins A, C, and E in rats with induced thyroid dysfunction. Twenty-one (21) rats were divided into three groups of 7 each: euthyroid (control), hypothyroid and hyperthyroid groups. Hypothyroidism was induced using 6-propyl-2-thiouracil (5 mg/100 g orally); hyperthyroidism was induced by daily intraperitoneal injection of L-thyroxine (0.1 µg/g). At the end of the experiment, rats were fasted for 12 hours and blood samples were collected under chloroform anaesthesia for the estimation of serum total triidothyronine (tT3), total tetraiodothyronine (tT4), thyroid stimulating hormone (TSH) and antioxidant vitamins A (retinol), C (ascorbic acid), E (α-tocopherol) using standard techniques. The results indicated significant decrease in tT3 (0.95±0.06ng/ml), tT4 (0.54±0.07 µg/dl) and increase TSH (0.13±0.00 µIU/ml) in hypothyroid, while there were significant increase in tT3 (2.60±0.21 ng/ml), tT4 (12.91±0.57 µg/dl) and decrease TSH (0.020±0.00 µIU/ml) in hyperthyroid compared with euthyroid rats (1.53±0.05 ng/ml, 3.62±0.25 µg/dl and 0.05±0.001 µIU/ml respectively). The serum levels of antioxidant vitamins A (1.77±0.07 µmol/L, 1.20±0.48 µmol/L), C (13.87±2.11 µmol/L, 25.63±1.59 µmol/L), and E (9.30±1.50 µmol/L, 12.34±1.82 µmol/L) were significantly (p<0.001) lower in both hypothyroid and hyperthyroid respectively compared with euthyroid rats (2.28±0.07 µmol/L, 44.69±1.62 µmol/L, 44.51±2.96 µmol/L respectively). A significant negative correlation was established between antioxidant vitamin A and tT3, and also between vitamin E and tT4 in hyperthyroid rats. The results confirmed the role of oxidative stress in hypothyroidism and hyperthyroidism and underscores the role of antioxidant vitamins A, C and E in delaying the consequence of hypothyroidism and hyperthyroidism or otherwise.